The natural colour of hemp and flax

FOR EACH SHIPMENT of yarn cones or fabric rolls, attention is given to the production or dye batch. Unlike synthetic fibres such as polyester, natural fibres like cotton, wool, linen, and hemp are subject to natural variations in their base colour. Even when processed and dyed using identical methods and recipes, minor colour differences may remain.

Such variations are even more pronounced in undyed, natural fibres. In particular, hemp and flax (linen) often display a wide range of natural shades. This variability results directly from the processing steps the fibres undergo before spinning.

Composition of hemp and flax fibres

The textile-grade fibres of hemp and flax are located in the stem of the plant and are recognized for their high tensile strength. Within the plant, these fibres provide structural integrity, flexibility, and protection for the vascular bundles (bast vessels) that transport water and nutrients. The fibres occur in bundles, encased externally by the plant’s cortex and internally by the phloem. They are bound together by pectin, a polymer within the cell walls that provides cohesion and rigidity.

To prepare the fibres for textile use, they first must be separated from surrounding tissues through a process known as retting. The most common method involves leaving the plants in the field for several weeks post-harvest, with periodic turning. Retting occurs through the combined action of rainwater, sunlight, and microorganisms that degrade the organic matter encasing the fibers. Soil conditions and climate directly influence both the duration and effectiveness of the process.

Retting also determines fibre colouration: fibres change progressively from green to straw-yellow, grey, or even black. Insufficient retting results in yellowish fibres, while excessive retting produces dark grey or black fibres.

The process is inherently difficult to control, as it relies on natural environmental factors and ceases only once the plants are fully dried. At that stage, the fibres can be baled and stored. In Northern Europe, hemp is particularly susceptible to over-retting, since it is harvested late in the summer, coinciding with wetter autumn conditions. Flax, harvested earlier in the season, is less affected. This explains why the natural colour of both hemp and flax varies significantly between harvest years and growing regions.

Batch blending

To achieve a more uniform appearance, fibre batches are blended at an early stage, prior to spinning. Lots from multiple years, regions, and even countries are combined based on colour characteristics. In some cases, harvests from more than twenty locations over a three-year period are blended, yet minor differences may still remain.

The larger the supply base, the greater the potential for achieving a consistent shade. Flax is advantaged in this respect, as it is cultivated on a much larger scale than hemp. Hemp offers fewer opportunities for blending, which often results in more pronounced color variations.

Due to this practice of multi-origin blending, it is generally not possible to trace with certainty the exact geographic origin of the hemp or flax contained in a particular yarn or fabric.